Engine cooling apparatus



Oct. 20, 1959 B. o. HOWARD ENGINE COOLING APPARATUS Filed Jan. 30, 1956INVENTOR. BEN O. How/4120.

United States Patent Dynamics Corporation, San Diego, 'Calif., acorporation of Delaware Application January '30, 1956, Serial No.562,156

Claims. (Cl. 123-4161) The present invention relates to engine coolingsystems and more particularly to an engine coollng system which embodiesbaflie means for directing a flow of cool- 7 mg arr.

Heretofore it has been common practice to cool engines, particularlyaircraft engines of the'internal combustion type, by causing a stream ofcooling air to flow against the forward portions of the enginecylinders, and subsequently changing the path of that airstream todirect it upon the rearward portions of the cylinders. This flow of airat the rear of the cylinders was necessary to dissipate the heatgenerated within the cylinders, which heat could not otherwise bedissipated by reason of the comparative inaccessibility of the rearcylinder areas to the cooling airstream. The prior art baffles generallyutilized to accomplish this end were formed to fit about the peripheryof the cylinders, or about the usual heat radiating fins thereof, at asubstantially uniform distance, with the air 'inlet and outlet openingsthus formed being fixed in size so that a predetermined quantity ofcooling air was permitted to flow therethrough. Since the amount of airallowed to enter is governed by the cooling requirements of the hottestcylinder areas, usually the rearward cylinder areas, the baliie openingswere adjusted to allow an amount of air to pass which was justsufficient to satisfactorily cool such hot areas. However, it will beapparent that to provide a sufficient flow of cooling air over thehotterrearward "portions of the cylinders (where the cooling air will behottest from having previously cooled the forward cylinder areas)requires that the quantity of air flowing over the forward cylinderareas be in excess of that needed at the forward areas. This results ininefiicient overcooling which in turn, it has been found, undesirablyincreases the aerodynamic drag upon the aircraft. in addition, it willbe apparent that cylinder areas intermediate the forward and rearwardareas also suffered from undesirable overcooling, the amount of suchoverco'oling depending upon their relative positions along the path ofthe airstream. Thus, the prior art baflies are ineffective to providesubstantially uniform cooling :of the engine cylinders, and theuncontrolled and inefficient utilization of cooling air is apparent.

In accordance wth the present invention, fairing or baffle means areprovided which are particularly adapted to fit about the usual finnedaircraft engine cylinder to provide uniform cylinder cooling. Thebaflle, which is preferably made insections, is spaced from the cylinderat various predetermined distances, these :distances each beingestablished in conformity with the local cooling requirements of'theparticular cylinder area with which that portion of the bafileassociated. Thus the available air mass flow at each areacan bepredetermined to fit the needs of such area. For example, it .can .becalculated "ice by known methods, using temperature measurements of thearea to be cooled, that a certain quantity of heat generated at thatarea must be dissipated in order to cool the area to some predetermined,desired operating temperature. Knowing the heat which must bedissipated, the baffle of the present invention is arranged adjacent thearea to be cooled at the particular distance therefrom which will'effecta speed of air flow corresponding to the heat transfer which should takeplace to achieve the desired cooling. The baflle distance is varied inaccordance with the individual heat transfer requirements of eachcylinder area to be cooled, as will be more particularly explainedhereinafter, whereby a most efficient utilization is made of theavailable quantity of cooling air. More particularly, at the coolerforward cylinder areas the baffle is spaced from the cylinder a distancesuch that the speed of the stream of cooling air is made comparativelylow with respect to the cylinder fins. However, by reason ment's :ofsuch local area.

of the present construction the speed of the cooling air isprogressively increased rearwardly so that a high speed cooling streamis provided at the hotter rearward fin areas. Also, a higher speed ofcooling airflow is provided in intermediate-cylinder areas to compensatefor the gradual heating up of the cooling air as it travels about thecylinder. Thus, a controlled utilization of the available cooling air isprovided, and the cooling air is used much more efliciently than was thecase with the cooling baflies of the prior art. The amountof cooling airrequired is greatly reduced, which in turn lowers the drag associatedwith the intake of the cooling air to thereby effect an improvement inthe overall performance of the aircraft.

'It is noted that although the cooling system of the present inventionwill be described in association with an air-cooled aircraft engine, itis obviously adapted to modification and is therefore to be consideredapplicable to various types of engines.

It is therefore an object of the present invention to provide an enginecooling system which is adapted to make a highly efficient utilizationof the available cooling medium.

7 Another object of the invention is to provide a unique cooling bafflewhich is adapted to be arranged adjacent to and spaced from a heatedsurface in a manner which will direct a predetermined mass flow of airagainst such surface for the cooling thereof to a substantially uniformtemperature throughout.

It is another object of the invention to provide a novel baffle fordirecting and controlling a predetermined mass flowof cooling air aboutan engine cylinder, and which is arranged along the cooling path of'theair to progressively effect anincrease in the speed of "flow of such airas the air passes toward the rearward areas of-such cylinder.

Still'another object of the invention is to provide a novel coolingbafile which is adapted 'to be spaced at various distances from'asur'face to be air-cooled, the distance of the baflle from each localarea of such surface progressively diminishing from the forward to therearward portions of :such surface along the path of the cooling :air inaccordance with the heat transfer require- An additional object of theinvention resides in the provision of an improved cooling jacket for anengine cylinder which is adapted to .be disposed about *the cylinder atpredetermined distances which are substantially available for cooling.

Yet another :object of the invention is the provision "of a novelcombination of a finned engine cylinder and a cooling jacket disposedthereabout in spaced relation, the distance therebetween being varied toadjust the speed of air mass flow over the cylinder cooling fins at eachlocal cylinder area so as to effect cooling of the cylinder to asubstantially uniform temperature.

Another object of the present invention is to provide an improvedcooling system which is comparatively simple in construction, easy toinstall, and economical to manufacture.

Other objects and features of the present invention will be readilyapparent to those skilled in the art from the following specificationand appended drawings wherein is illustrated a preferred form of theinvention, and in which:

Figure 1 is a side elevational view of the preferred em- "bodiment ofthe cooling system of the present invention,

illustrated in association with a conventional aircraft cylinder; Figure2 is a front elevational view of the invention illustrated in Figure 1;

Figure 3 is a view taken along line ILL-III of Figure 1;

and

Figure 4 is a diagrammatic representation of the cooling arrangement ofFigure l and of a common cooling arrangement of the prior art, togetherwith comparative temperature gradient curves to indicate temperaturesalong the path of the cooling air. Referring to the drawings and moreparticularly to Figures 1 and 2, there is illustrated an embodiment ofthe cooling system of the present invention which will hereinafter bedescribed in connection with the cooling of a typical aircraft radialinternal combustion engine. It is to be understood, of course, that theembodiment described is merely illustrative of a particular applicationand the present invention is not to be limited thereto.

A cylinder of the engine is designated generally by the numeral 11, andis characterized by the usual and conventional construction of a typicalair cooled aircraft engine cylinder. Cylinder 11 is rigidly secured, asby nuts 12 threaded onto engine studs 13, to an engine crankcase 14 ofthe engine. Other cylinders are similarly secured to crankcase 14, andthe cooling of cylinder 11 and the other cylinders is effected bypermitting a flow of cooling air to be directed upon the forward facesof the cylinders and guiding that flow in a particular manner around andbehind the cylinders, as will be more particularly describedhereinafter.

The flow of cooling air, which may be ram air or air provided by anysuitable source, passes about the cylinders, picking up and carryingaway excess heat, and finally passes from behind the cylinders into theairstream at an exit temperature considerably higher than its inlettemperature. The technique of individually air cooling a plurality ofengine cylinders is well-known in the art and for this reason will notbe described in any great detail. In-

stead the present invention will be described in connection with thecooling of the single engine cylinder 11, it being understood of coursethat the present cooling system described in connection with cylinder 11is readilyadapted for similar association with other engine cylinders,which cylinders are arranged either in a single or a double bank, or inradial or in-line relationship, for the eflicient cooling of a completeengine.

Cylinder 11 is of usual construction and embodies a barrel portion 15and a head portion 16, portion 15 being 17, and portion 16 beingprovided with a plurality of usual vertical cooling fins 18. Fins 17 and18 are commonly varied in depth according to the amount of heatgenerated in the area with which they are associated, the deeper finshaving a greater surface area whereby they are adapted to transfer agreater quantity of heat from cylinder 11 to the cooling airstream, ascompared to the shallower fins which transfer less heat for the samespeed of provided with a plurality of usual horizontal cooling fins r 4airstream. Cylinder 11 also includes one or more spark plugs, one ofwhich is indicated at 19, and a pair of valve rocker boxes 21 and 22 forhousing and supporting the conventional valve operating mechanism forcylinder 11. Boxes 21 and 22 are an integral part of cylinder 11, exceptfor removable cap portions thereof which permit access to the valvemechanism, whereby boxes 21 and 22 are adapted to provide rigid supportfor portions of a baflie means or assembly 23, as will be seen.

Bafile assembly 23 serves to accept a portion of the cooling airstreamflowing against the face of cylinder 11, and guide that portion aboutcylinder 11 and over fins 17 and 18 thereof in a manner calculated toderive the maximum cooling effect from the action of such given portionof cooling fluid flowing over fins 17 and 18 and about cylinder 11.

Baflleassembly 23 comprises, a pair of side baflles or bathe sections 24and 25, which are disposed about cylinder 11 at the sides thereof inclose association with cooling fins 17. Assembly 23 also comprises anupper or top bafile or baflle section 2.6, which is disposed over thehead portion 16 of cylinder 11 in close association with cooling fins18. With this arrangement it will be apparent that the frontal openingsformed by cylinder 11 and the forward or upstream edges of baffle means23 provide an inlet for a limited quantity of cooling air, which issubsequently distributed by baffle means 23 about cylinder 11.

Side baflles 24 and 25 are each secured at their upper ends to cylinder11 by a plurality of nuts secured to bolts 27 which are disposed throughsuitable openings in baffles 24 and 25 and threaded into tapped wells incylinder 11. At their bases, bafiles 24 and 25 are secured together andsupported upon cylinder 11 by a circumferential band or strap 28 whichencircles cylinder 11 at its base. Strap 28 passes over the lowerperiphery of bafiles 24 and 25, and is provided with a fastening means,such as bolt and nut connector 29, to clamp bafiles 24 and 25 inposition. In addition, a peripheral band or spacer 31 is carriedapproximately midway of barrel portion 15 of cylinder 11 betweenadjacent fin sections, spacer 31 being positioned between barrel portion15 and bathe sections 24 and 25 to maintain a fixed, spaced apartrelationship therebetween. It will be apparent that the width of spacer31 is made to conform to the distance which is desired to be maintainedbetween portion 15 and sections 24 and 25 for a particular speed of airflow. Spacer 31 includes a pair of arcshaped side members 32 which aredisposed on either side of cylinder 11, members 32 being joined at therear of cylinder 11, Figure 3, by-a short strap 33 removably securedthereto by bolts 34.

Upper baffle 26 is secured in position by a plurality of nuts 35 whichare threaded onto the free ends of studs 36, whose lower ends aresuitably threaded into the material of rockerboxes 21 and 22 and withtheir upper, or free, ends disposed through appropriate apertures inbaflle 26. Baflle 26 includes a transverse member 37 which serves tostrengthen baflie 26 and maintain the shape thereof, it being noted thatmember 37 is suitably cut away at 38 to accommodate ignition wiring (notshown).

In order to establish an air path of a particular size, it will be seenthat baflle means 23' is shaped to closely conform to the irregularitiesof cylinder 11, and that the exit ends of bafile sections 24, 25 and 26are flared outwardly slightly to effect a smoother discharge of coolingair and thereby reduce the aerodynamic drag associated with such part ofcylinder 11, the common solution was'to increase the quantity of coolingair, as by merely making uniformly greater the distance between cylinder11 and prior art baffle 39. This admittedly provided a greaterflow ofcooling air but, obviously, .the arrangement of baffle 39 effected anovercooling of cylinder areas which may previously have been properlycooled. In addition, 1as"illustrated by the temperature gradient line41, the temperature of fin 17 becomes gradually greater when usingbaflle 39 because the same size air flow path is present from theupstream to the downstream end, and the speed of air flow is thereforesubstantially constant. Since the air is absorbing heat from fin 17 allthe time, it has less capacity to remove heat at the downstream end ofbaffle 39 and fin 17 consequently, rises in temperature. It is apparentthat with this non-uniform temperature distribution pattern that forwardcylinder areas must be over cooled in order to achieve proper cooling ofthe rear cylinder areas. As previously stated, this not only inducesundesirable drag, but also produces poor engine performance.

In contrast, baflie section 25 of the present invention adjusts the sizeof the air flow path to thereby adjust the speed of air flow and effecta uniform temperature pattern, as indicated by temperature gradient line42. More particularly, the well-established relationship among theVariables present in the cooling of cylinder 11 is as follows:

a re ny" is r k h=heat transfer coefiicient where d=distance aroundcylinder 11 k=heat conductance K=constant fixed by the units ofmeasurement used V=speed of air moving around cylinder =air viscosity C=air specific heat =air density For temperature changes of the order ofto 300 degree Fahrenheit normally encountered in engine cooling thevariables k, p, ,u, C and K are substantially unchanged and remain intheir effects substantially constant, so that where Q=the time rate ofheat flow per unit area h=heat transfer coeflicient =temperature of theheated surface T =temperature of the air then the value of h is adjustedso that Q is substantially the same at all points around the cylinder,whereby uniform cooling is produced over the entire cylinder. Theadjusted value of h will, of course, determine the requiredcrosssectional area between cylinder 11 and baffle section 25.

In the above manner the particular proportions or dimensions of bafflemeans 23, and the arrangement thereof with respect to cylinder 11, ispredetermined. Typically, baffle means 23 closes or converges rearwardlyto provide a passage for the cooling air which is progressivelydiminishing in cross section whereby the air speed is progressivelyincreasing. The cooling system of the present invention thus utilizesthe relationship of cylinder temperatures, cooling air temperatures, andcooling air velocities to provide baffle means 23' of a configurationwhich varies in accordance with the cooling requirements of local areasofcylinder 11 .so that maximum cooling efficiency is derived from theincoming cooling air. It will be apparent that the improved efiiciencyresulting from use of the present cooling system permits a desirablereduction in the frontal area of the cooling system, and this results ina corresponding increase in the performance characteristics of theaircraft.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims:

I claim:

1. In a cooling system for an engine, baffle means forming an air flowpath with an engine surface to be cooled, said bafile means beingcontoured and spaced to provide a time rate of heat flow per unit area,Q, Which remains substantially the same along the air flow path inaccordance with the following formula:

where T =temperature of said surface, T =temperature of the air, andh=heat transfer coeflicient which is related to speed V by the formula:h=Kd-'- V- where K=a constant, and d=a distance along the air flow pathand V=velocity at any point along said path.

2. In combination with a surface to be cooled, baffle means, meansspacing said bafiie means in predetermined relationship with saidsurface to form an air flow path with said surface, said bafile meanshaving a contoured inner surface for varying the cross-sectional area ofsaid air flow path to thereby vary the heat transfer coefficient, h, inaccordance with the following formula: h=K d- V where K =a constant,d=distance along the air flow path, so that the time rate of heat flowper unit area, Q, remains substantially the same along the air flow pathin accordance with the following formula: Q=h(T T where T =temperatureof said surface, T =temperature of the air.

3. In combination with a cylinder of an air-cooled internal combustionengine, a baflle assembly comprising a pair of side bafiies, one carriedat each side of said cylinder, and an upper baffle carried adjacent thehead of said cylinder, means for disposing said side bafiles and saidupper baffle adjacent to said cylinder in predetermined spacedrelationship therewith to form air flow spaces therebetween, saidbaffles having inner surface contours such that the area of said airflow spaces changes along the air flow path to establish a substantiallyuniform heat flow per unit area, said heat flow per unit area being afunction of the heat transfer coeflicient of said path which iscontrolled by air velocity which in turn depends upon said area of saidair flow spaces.

4. In combination with a finned cylinder of an aircooled internalcombustion engine, a baffle assembly comprising a pair of side baflies,one carried at each side of said cylinder and each spaced from the finsof said cylinder to define an unobstructed air induction area with saidcylinder, and spacer means interposed between said side baffles and saidcylinder to maintain spaced rela tionship therebetween, an upper balflecarried adjacent the head of said cylinder, said side bafiles and saidupper baffle being shaped and spaced from said cylinder in predeterminedmanner to define substantially unobstructed air flow passages whose areais adjusted along the air flow path to maintain a substantially uniformheat flow per unit area.

5. In combination with a surface to be cooled, a baffie of such irmershape and spacing from said surface such that air passing therebetweenwill change in velocityin accordance with the following formula:

V- g j 2,424,416

8 a 6 where V is the air velocity which determines the spacing desired,Q=the time rate of heat flow per unit area and is held constant alongthe air flow path, K=a constant, 332,957 d=distance along the air flowpath, T =temperature of 942,119

said surface, and T =temperature of the air.

. References Cited in the file of this patent UNITED STATES PATENTS PiryJuly 22, 1941 FOREIGN PATENTS" Italy Dec. 12, 1935 Germany Apr. 26, 1956

